The present invention relates to tires intended for off-road use on loading, earth-moving and transportation equipment, for example, equipment used in quarries or underground mines. Such tires have a radial carcass reinforcement and a crown reinforcement formed of at least two superimposed plies of cables forming an acute angle with the circumferential direction.
Tires of this type operate under severe conditions of load, and they travel on ground strewn with cutting objects (blocks of stone having sharp edges, metal objects, etc.) and often in mud and water. These cutting objects initiate numerous cuts of scratches on the tread and sidewalls of the tire. The cuts and scratches are propagated more or less rapidly in length and depth under the effect of the repeated flexures of the tire. The cuts and scratches increase in length and depth as a function of their number, their initial depth and length, their direction and the distance between them, and ultimately they may reach the radial carcass reinforcement and cause relatively rapid destruction of the reinforcement or result in loss of rubber and rapid degradation of the sidewalls.
In order to reduce the risk of damage to the side-walls of a tire, it has heretofore been proposed in French Pat. No. 1,452,787 that the region of the sidewall close to the thread, that is, the shoulder region, be provided with a protuberance which protrudes with respect to all portions of the sidewall under severe conditions of load. The radially outer face of said protuberance forms an angle of 70.+-.10 degrees with the transverse direction, and the maximum axial width of the tire is then located at a distance h, measured from the crown of the tire, equal to about 1/4 of the total height H of the tire.
Such protuberances are particularly effective against the propagation of cuts caused by protruding rocks on the surface of the ground or the side surfaces or walls of the underground galleries. However, as the cuts are concentrated on these protuberances, the protuberances rapidly become ineffective due to their rapid destruction by degradation, such as wear and tearing. As the distance d, the difference between the maximum axial width and the nominal axial width of the tire under load, becomes negative, the sidewall of the tire loses its protection at the level of the nominal axial width.
It is also well known that the sidewalls of tires, particularly tires of vehicles which make frequent stops along the curb of sidewalks, can be protected by circumferential bands or protective ribs, for example, as disclosed in French Pat. No. 2,131,874. These bands or ribs are located substantially at the mid-height of the sidewall of the tire and withstand wear by rubbing or scraping. On the other hand, when they come into contact with cutting objects, these bands or ribs, due to their location, are subject to numerous and severe cuts which extend and enlarge rapidly and so are unsuitable for tires of the type with which the present invention is concerned.